The present invention relates to a vehicle door latch device, and more particularly to a vehicle door latch device provided with a one-motion door opening mechanism and an antitheft mechanism.
A conventional vehicle door latch device is provided with a lock lever which is displaceable, by an unlocking operation and a locking operation of an inside lock button of the door, between an unlocked position where an opening operation of an outside open handle of the door is transmitted to a ratchet so as to open the door and a locked position where the opening operation of the outside open handle is not transmitted to the ratchet. Because the inside lock button to which the lock lever should be connected is disposed on an interior surface of the door in the exposed state, an antitheft performance of the lock button is not so high. For example, it is quite easy to operate the lock button by breaking a door glass from outside the vehicle to illegally change the lock lever to the unlocked position. To invalidate such an illegal access to the lock button, a number of antitheft mechanisms have been developed.
The typical antitheft mechanism has a free-play mechanism provided between the inside lock button and the lock lever (e.g., U.S. Pat. No. 5,538,298). The free-play mechanism can absorb an unlocking movement of the lock button so as not to transmit the unlocking movement to the lock lever. That is, no external force is applied to the lock lever even if the lock button is operated to unlock illegally. This free-play type antitheft mechanism effectively invalidates the illegal access to the inside lock button.
The prior art free-play type antitheft mechanism has a disadvantage that it cannot easily be combined with the well known one-motion door opening mechanism which carries out restoration of the lock lever from the locked position to the unlocked position and opening of the door substantially at the same time, by the opening operation of the inside open handle. The one-motion door opening mechanism transmits an opening movement of the inside open handle to the lock lever located in the locked position in order to return the lock lever to the unlocked position. Due to this mechanism, even if the inside lock button is protected by the antitheft mechanism, the illegal access can unlock the lock lever easily.
Accordingly, it is an object of the present invention to provide a vehicle door latch device with addition of a free-play type antitheft mechanism and a one-motion door opening mechanism by overcoming the above mentioned disadvantage.